Liverpool's Georginio Wijnaldum in action with Arsenal's Aaron Ramsey
Liverpool left London all smiles after a thrilling second half saw them come from behind to deal a crushing defeat on Arsenal.
The Gunners were 1-0 up in the 31st minute when Theo Walcott, who had a penalty saved a minute before, confidently slotted in a pass from Alex Iwobi after exploiting the space left behind by Alex Moreno.
Liverpool had been poor for in the opening half, but went in level at the break thanks to a stunning free-kick from Coutinho in stoppage time.
It was the Reds that came out quickest in the second period and they were ahead in the 49th minute when Adam Lallana finished off a well worked move with a well taken finish.
Coutinho then added a third in the 56th minute and Liverpool were 4-1 up seven minutes later when Sadio Mane scored a fine individual goal on his debut.
There was an instant reply from Arsenal when Alex Oxlade-Chamberlain cut inside and shot, a deflection taking it past Simon Mignolet.
And despite a 75th minute header from Callum Chambers, Liverpool held on as Arsenal lost their opening game of the season at the Emirates for the third time in four season.
Here are five things learned from the fixture:
Game of two halves
It is such a cliche, but this game reminded us that football really is a game of two halves.
Arsenal completely dominated the first 45 minutes barely giving Liverpool a sniff. Walcott was running rings around Moreno and earned a penalty, before Mignolet saved the England wingers attempt.
Arsene Wenger felt the sucker punch with Coutinho's free-kick but he would not have expected the Reds to come out as they did in the second half.
Moreno lost in defence
Alberto Moreno had a torrid time in Liverpool's Europa League final defeat to Sevilla as some high-profile mistakes led to the Spanish side's goals.
It was no different today, his first competitive match since. In the 14th minute he headed towards Aaron Ramsey before sprinting and lunging in on the Welshman to concede a corner.
He then gave away the penalty as Walcott nipped the ball past him. And a minute later, despite the let-off, he was responsible again as he left the ex-Southampton player in space leading to the opening goal.
His defensive qualities are inept and he looks more comfortable further forward. James Milner missed out due to injury but surely Moreno is on borrowed time at Anfield.
Search for a defender goes on
For just the second time in four years, Arsenal went into a Premier League fixture without either Laurent Koscielny or Per Mertesacker.
Both were missed as the young partnership of Chambers and debutant Rob Holding failed to deal with the speed in Liverpool's attack.
All three second-half goals for Liverpool were well-worked moves. However, a leader would have helped to keep some composure and calmness at the back.
Wenger will be hoping a move for Germany international Shkodran Mustafi can be completed sooner rather than later.
And maybe a forward too
Where Arsenal now find themselves chasing a defender, they may have wasted time in their annual summer search for a prolific goalscorer.
They failed with moves for Gonzalo Higuain, Arkadiusz Milik and Wissam Ben Yedder and are stuck in negotiations for Alexandre Lacazette. Today, the Frenchman scored a hat-trick for Lyon.
Alexis Sanchez started through the middle against Liverpool and was ineffectual. Olivier Giroud didn't feature.
It is time for Arsenal to show their wealth by opening the coffers to sign a world-class centre forward.
Klopp loves the occasion
Jurgen Klopp is a gun-ho manager. He may lost the two finals he has managed in his short time at Liverpool, against Manchester City in the League Cup, and Sevilla in the Europa League.
But his team started this season in a similar fashion to the way they played at times last year.
He did the double over Man City, winning 3-0 at Anfield and 4-1 at the Etihad. In his only Merseyside derby, he beat Everton 4-0.
He has also beaten Manchester United 2-0 and then there was that stunning 4-3 comeback against ex-club Borussia Dortmund.
Not the only 4-3 comeback in his Liverpool career...